Effect of thermal treatment on the fatigue crack propagation behavior of a new Ni-base superalloy

The effect of various thermal treatments, including direct aging, pre-treatment, and long-term exposure, on the hold-time fatigue crack propagation behavior of 718Plus alloy were investigated and the results are summarized as follows: (1) The hold-time fatigue crack propagation rates (FCPRs) of the direct aged (DA) sample is almost the same as that of the 718Plus alloy after conventional solution plus age heat treatment. The FCP of the DA sample is slower than the conventional 718Plus alloy at 650 °C, under 3S loading condition; (2) the long-term exposure tests show that the alloyʹs hold-time fatigue crack resistance is improved after being exposed at 760 °C for 350 h; (3) the fine-grain alloy shows better hold-time FCP resistance than coarse-grain alloy, which is attributed to the δ-phase effect; and (4) after pre-treatment at 857 °C for up to 24 h, the alloyʹs fatigue crack resistance is improved because of the δ-phase at the grain boundaries.